llvm dev - Apr 2018 - How to create and insert a call MachineInstr?

Hi all,
I am working on a project which needs to create and insert a MachineInstr
which calls a function. But I don't know how to build it. The function has
been declared in IR.
I have used BuildMI to build a MachineInstr. But it seems that a call
MachineInstr only has one parameter which is a
register(%physreg44<imp-use>?). Therefore how can I set the callee
function
and the arguments of the function?
Thanks a lot,
Will
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://lists.llvm.org/pipermail/llvm-dev/attachments/20180413/e088cb06/attachment.html>

Hi Will,

On 13 April 2018 at 09:50, Will Lester via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
> I have used BuildMI to build a MachineInstr. But it seems that a call
> MachineInstr only has one parameter which is a
> register(%physreg44<imp-use>?).
This depends on the target, but calls normally have a few operands:

  + The callee (a register or a global address or something).
  + A regmask indicating which registers the call preserves.
  + A list of imp-uses and imp-defs for the registers used to pass and
return parameters.

If you writie a .ll file that makes a call you should be able to see
all these components in the generated MIR.
> Therefore how can I set the callee function and the arguments of the
function?
For a direct call, you'd normally use MachineInstrBuilder's
addGlobalAddress to set the callee. You have to emit separate moves
and stores before the call to put the arguments in the correct
registers and stack slots. Be careful not to clobber live registers!

We can probably give a few more details (like the call instruction to
use, and which registers pass parameters; maybe some extra quirks) if
we know the actual target you're compiling for, but the outline above
won't change significantly.

Cheers.

Tim.

Thanks for your help! I'm much more clear about this problem.
Will

2018-04-13 17:53 GMT+08:00 Tim Northover <t.p.northover at gmail.com>:
> Hi Will,
>
> On 13 April 2018 at 09:50, Will Lester via llvm-dev
> <llvm-dev at lists.llvm.org> wrote:
> > I have used BuildMI to build a MachineInstr. But it seems that a call
> > MachineInstr only has one parameter which is a
> > register(%physreg44<imp-use>?).
>
> This depends on the target, but calls normally have a few operands:
>
>   + The callee (a register or a global address or something).
>   + A regmask indicating which registers the call preserves.
>   + A list of imp-uses and imp-defs for the registers used to pass and
> return parameters.
>
> If you writie a .ll file that makes a call you should be able to see
> all these components in the generated MIR.
>
> > Therefore how can I set the callee function and the arguments of the
> function?
>
> For a direct call, you'd normally use MachineInstrBuilder's
> addGlobalAddress to set the callee. You have to emit separate moves
> and stores before the call to put the arguments in the correct
> registers and stack slots. Be careful not to clobber live registers!
>
> We can probably give a few more details (like the call instruction to
> use, and which registers pass parameters; maybe some extra quirks) if
> we know the actual target you're compiling for, but the outline above
> won't change significantly.
>
> Cheers.
>
> Tim.
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://lists.llvm.org/pipermail/llvm-dev/attachments/20180413/277003c1/attachment.html>